448 



REPORT — 1895. 



at 30 feet above the ground, was directed. On the outer end of the 

 radial arm was an adjustable pointer, the sharp edge of which was set to 

 almost touch the plumb-line. The rods were slowly lowered for .30 feet, 

 with every endeavour to avoid rotation, but if the radial pointer did 

 deviate at all from the plumb-line, this was corrected by gently twistino- 

 the rods. A second radial arm, exactly similar to the first, was then 

 clamped on at 30 feet higher up, and its pointer accurately set to the 

 line, after which the lower one was removed. This was repeated until 

 the marking tool reached the core, and in returning to the surface the 

 process of fixing and unfixing the radial arms was performed in reverse 

 order. 



The form of apparatus to be used for establishing a connection between 



Fig. 8. 





Scale, I iu. to 2 ft. 



the marked diameter on the crown or tube and the unbroken rock, next 

 claimed attention. Whatever method might be adopted, it was obvious 

 that it was only whilst the rock was in situ that this relation could be 

 determined, and consequently the greatest care would be necessary to 

 ensure that any core operated upon had not been broken oS" during the revo- 

 lution of the boring crown. At Ware, the first trial was made in the follow- 

 ing manner. Three steel V-shaped cutters (fig. 10) were fixed on the inside 

 surface of a boring crown, at a distance of H inches from its lower end, 

 and with their cutting edges at such a distance from the axis of the crown 

 as was about ^ of an inch less than the I'adius of the core, whose diameter 

 was 13^ inches. One of these cutters was set on the line of diameter 

 indicated by the notches on the outside of the crown, and the other two 

 cutters were placed at equal distances from the same line on the opposite 



